1. Technical Field
This invention relates in general to mobile computing electronic devices and, more particularly, to a method and apparatus for wireless communications between mobile computing electronic devices.
2. Description of the Related Art
Mobile computing electronic devices, such as electronic calculators and portable computers, have evolved significantly in recent years. In addition to arithmetic calculations, current day calculators often provide programming and graphing functions. Graphing calculators include a screen able to display graphics in addition to alphanumeric characters. Portable computers, on the other hand, are progressively becoming more mobile, as the weight of the computer is reduced, while maintaining processing capabilities at the same level as desktop computers.
For some time, graphing calculators and portable computers have been able to communicate to one another through a wired connection. An example of a calculator of this type is the TI-92 calculator produced by Texas Instruments Incorporated of Dallas, Tex. Wired connections may be used, for example, in a classroom setting where problem sets are downloaded from the teacher's calculator to the students' calculators. Once downloaded, the students can use the calculator to solve the problem. Teacher's can review the student's answers in real-time to determine which students are having difficulty solving the problems.
Portable computers also can communicate through computer networks. Recently, wireless networks have become available for computers. A great advantage of a wireless network is the ability to maintain a network connection within a defined area with a portable computer without losing the mobility of the computer. Wireless networks for graphing calculators have been proposed in U.S. application. Ser. No. 08/706,123 to Siep et al, filed Aug. 30, 1996, entitled "Active Wireless Network For Calculators," U.S. application. Ser. No. 08/707,165 to Siep et al, filed Aug. 30, 1996, entitled "Passive Wireless Network For Calculators," U.S. application. Ser. No. 08/697,808 to Siep et al, filed Aug. 30, 1996, entitled "Method of Implementing a Network in a Classroom Setting," and U.S. application. Ser. No. 08/753,563 to Siep et al, filed Nov. 26, 1996, entitled "Method and Apparatus for Low Power Communications Between Mobile Computing Devices," all of which are incorporated by reference herein.
Despite the advantages of networks in non-commercial setting such as classrooms, they have not been accepted in widespread use. Wired connections between calculators is somewhat inhibiting to the students. Wireless communications in a classroom or auditorium has several problems. First, in order to have effective communication between the teacher and the students, the student devices must have sufficient battery power to transmit a signal that will reach the teacher's calculator. Unfortunately, designing student devices with enough transmitted power to reach the teacher's desk in a normal sized classroom would deplete the smaller calculator batteries at an unacceptable rate. This is a particular problem with calculators which have relatively small batteries and would, without the wireless communications, last for approximately eight months. Adding wireless communications could decrease the battery life to a single month or less in normal use. Second, it is desirable that the devices operate in a frequency band which is designated as unlicensed by the FCC (Federal Communications Commission). In order to prevent interference between devices operating in an unlicensed frequency band (the ISM--Industrial, Scientific and Medical--band), the FCC has strict guidelines on the spread spectrum modulation schemes which must be used, if the devices broadcast at a power equal or greater than 0.7 milliwatts. Current day wireless transmission devices must exceed this level to accurately communicate over distances up to thirty meters; therefore, they must use a spread spectrum modulation scheme approved by the FCC which increases the complexity, cost and power consumption of the system.
Accordingly, a need has arisen in the industry for a low cost, low power, method and apparatus for communicating between mobile computing electronic devices.